Expand description
Schema-declared Json columns need a model-struct field type that’s the
same on every backend so the same struct compiles on server and on
embedded (including wasm32-unknown-unknown, which can’t depend on sqlx).
This newtype lives in cratestack-core so every backend can reference it
without introducing a cyclic dep. cratestack-sqlx provides the sqlx
Type / Encode / Decode impls on native targets.